• Proceedings of the Korea Concrete Institute Conference
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• 1993.04a
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• pp.65-72
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• 1993

Steel fiber reinforced concrete(SFRC) which is made by short, randomly distributed steel fibers in concrete is superior in its tensile mechanical properties to plain concrete in enhancement of tensile strength and tensile ductility. These improvements are attributed to crack arresting mechanism and formation of longer crack paths due to fibers , which as a consequence lead to increase in energy absorption capacity of SFRC. In the post-peak region under tensile stresses, major macrocrack forms at critical section. The opening of this macrocrack is mainly resisted by both of the fiber pull-out bridging the cracked surfaces and the resistance by matrix softening. In this study, micromechaincal approach has been made in order to simulate tensile behavior of SFRC and based on which the theoretical model is presented. This model reflects the features of both the composite material concept and the spacing concept in predicting tensile strength of SFRC. The model also takes into account for the effects of matrix tensile softening and fiber bridging by pull-out on the resistance for the post-peak behavior of SFRC. It has been shown that the developed model satisfactory predicts the experimental results.

• Proceedings of the Korea Concrete Institute Conference
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• 1994.10a
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• pp.291-300
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• 1994

The influence of elevated temperatures on the mechanical properties of concrete is important for fire-resistance studies and also for understanding the behavior of containment vessel, such as nuclear reactor pressure vessels, during service and ultimate condition. The present study is to clarify the damage/deterioration of concrete structures that are subjected to high temperature exposure. To this end, comprehensive experiments are conducted. The major test variables are the peak temperatures, rate of temperature increase, and sustained duration at peak temperature. The results include weight loss residual compressive strength and stress-strain curve. From those results, residua compressive strength formula and stress-strain relationship are proposed.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2007.11a
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• pp.45-48
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• 2007

This study investigates mechanical properties of the concrete using coarse particle cement which is manufactured by the classifying process. The variable factors are 3 types of W/C such as 40, 50, and 60% and 5types of the replacement of the coarse particle cement such as 0, 25, 50, 75, and 100%. As the results, amount of SP agent to secure the target fluidity is gradually declined in accordance with increasing CC replacement. There is no special tendency for target air content, but setting time is delayed according to increasing CC content. The peak of the simple adiabatic temperature rise is gradually decreased in accordance with increasing CC content, and approach time to peak is slightly delayed. The compressive strength is comparatively delayed.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2011.05a
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• pp.11-12
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• 2011

This study examine Effect of Change of Compressive Strength of Concrete Members with Insulating Gang form on Temperature History of Concrete Positions. Test show, insulating gang forms differences and gang forms have 10℃ on peak point temperature of surface and Center if temperature history have 24Mpa by change of compressive strength. In addition, there have 14℃(16℃) on peak point temperature of surface and Center if temperature history have 40(60)Mpa. Therefore, insulating gang forms have an effect insulating performance.

• Journal of the Korean Society for Railway
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• v.6 no.2
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• pp.81-86
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• 2003

This study proposes the neural network simulator for the integrity evaluation of weld zone in railway rails. For these purposes, the ultrasonic signals for defects(crack) of weld zone in frames are acquired in the type of time series data and echo strength. The detection of the natural defects in railway truck is performed using the characteristics of echodynamic pattern in ultrasonic signal. And then their applications evaluated feature extraction based on the time-frequency-attractor domain(peak to peak, rise time, rise slope, fall time, fall slope, pulse duration, power spectrum, and bandwidth) and attractor characteristics (fractal dimension and attractor quadrant) etc. The constructed neural network simulator agrees fairly well with the measured results of test block(defect location, beam propagation distance, echo strength, etc). The Proposed neural network simulator in this study can be used for the integrity evaluation of weld zone in railway rails.

• Journal of the Korean Society of Physical Medicine
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• v.4 no.3
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• pp.175-182
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• 2009

Purpose：The purpose of this study is to investigate the effects of Taekwondo training causing leg-muscular strength for elementary school children. Methods：The subjects were Taekwondo group (n=20) and non-Taekwondo group (n=20) from 5-6 graders of elementary school. The Tkd group exercised Taekwondo and the non-Taekwondo group exercised free gymnastics. The subjects were measured 3 times(pre, mid and after)during the 8weeks program. The leg muscular strength peak torque and average power were measured. And the extension-flection of angular speed 60 deg/sec and 180 deg/sec was measured. Results：The results of this study can be summarized as follows: 1. Compared with the Tkd group, the non-Tkd group showed no significant difference in tests statistically in case of right-left of pre-4weeks. The leg muscle's peak torque did not show significant difference in the extension angular 60 deg/sec(p>.05). 2. The score of flection angular speed 60deg/sec was not different in tests leg strength of right-left to pre-4weeks(p<.05), but the muscle was increased according to the amount of time spent in case of the 4-8weeks. 3. Compared with the Tkd group, the non-Tkd group showed no significant difference in tests statistically in case of right-left of pre-4weeks. The leg muscle's peak torque did not show significant difference in the extension angular 180deg/sec(p>.05). The right leg muscular strength was increased in case of the 4-8weeks. The left leg showed no difference. 4. Leg muscular strength was increased in the case of the pre-4weeks in the right of flection angular speed 180deg/sec. The left did not show difference. The right leg muscle in case of the 4-8weeks showed no difference. The left showed significant difference. Conclusion：Taekwondo training is effective for leg-muscular strengthing for elementary school children.

• Clinics in Shoulder and Elbow
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• v.13 no.1
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• pp.53-57
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• 2010

Purpose: The goal of this study was to evaluate differences in strength deficits between (i) patients with stage 1 or 2 impingement syndrome and (ii) patients with rotator cuff tears. Materials and Methods: We enrolled 43 patients with stage 1 or 2 impingement syndrome (group 1) and 21 patients with rotator cuff tears (group 2). The isokinetic strength of both groups was evaluated at $60^{\circ}/sec$ for external rotation, internal rotation, adduction and abduction. We measured the peak torque, total work, average power of bilateral sides, peak torque relationship to body weight, and the ratio between unilateral agonist and antagonist. Results: The isokinetic strength deficits assessed in ratio of peak torque to body weight for group 1 and group 2 respectively were; $28.48{\pm}23.76%$ and $29.12{\pm}32.81%$ for abduction (p=0.929), $7.20{\pm}13.98%$ and $18.94{\pm}19.52%$; for adduction (p=0.021), $16.88{\pm}13.76%$ and $25.80{\pm}24.07%$; for external rotation (p=0.221), and $14.1{\pm}25.67%$ and $29.02{\pm}35.06%$ for internal rotation (p=0.059). For average power and total work, group 2 showed a significantly greater deficit for adduction and internal rotation than group 1. Conclusion: Those with rotator cuff tears have more isokinetic muscle strength deficits than those with stage 1 or 2 impingement syndrome. Progression from stage 1 and 2 impingement syndrome to stage 3 may result in greatest changes in strength deficits for internal rotation and adduction.

• Journal of Korean Academy of Nursing
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• v.45 no.1
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• pp.35-45
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• 2015

Purpose: This study was done to determine whether muscle strength training programs have an impact on improving symptoms of urinary incontinence (UI) and physical function among elderly women with UI who reside in long-term care facilities. Methods: A randomized controlled trial was conducted. Participants had to be over 65 years, score over 15 score on the mini-mental state examination, and be able to walk alone or with an assistant. Seventy residents were randomly allocated to either the training group (n=35) or control group (n=35). The program consisted of 50 minutes, twice a week for 8 weeks, and included Kegel's exercise, Thera-band training and indoor walking. Main outcomes were UI symptoms, peak vaginal pressure and physical functions measured with timed up and go test (TUG), one leg standing test (OLST), activities of daily living (ADL) and grip strength. Changes in outcome measurements were calculated from baseline to 4 weeks and to 8 weeks using repeated measures ANOVA. Results: There were significant differences in peak vaginal pressure (p<.001), TUG (p<.001), OLST (p=.012) and grip strength (p<.001) in the interaction between groups and time. Conclusion: Future studies are suggested to confirm the effect of muscle strength training in long-term care facilities where elderly women with UI reside.

• Korean Chemical Engineering Research
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• v.46 no.2
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• pp.389-396
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• 2008

The effect of thermal cycling on bond strength and residual stress at the interface between benzocyclobutene (BCB) and plasma enhanced chemical vapor deposited (PECVD) silicon dioxide ($SiO_2$) coated silicon wafers were evaluated by four point bending and wafer curvature techniques. Wafers were bonded using a pre-established baseline process. Thermal cycling was done between room temperature and a maximum peak temperature. In thermal cycling performed with 350 and $400^{\circ}C$ peak temperature, the bond strength increased substantially during the first thermal cycle. The increase in bond strength is attributed to the relaxation in residual stress by the condensation reaction of the PECVD $SiO_2$: this relaxation leads to increases in deformation energy due to residual stress and bond strength.

• Journal of the Korean Ceramic Society
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• v.56 no.5
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• pp.489-496
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• 2019

Cement-based thermal insulation material was manufactured using OPC, lime, anhydrite, and CSA cement in this study. The morphology and physical properties of the material were analyzed using XRD. All samples had ettringite, Ca(OH)₂, and CaCO₃ crystals. The XRD peak intensity of the ettringite and Ca(OH)₂ slightly increased with an increase in curing time from 3 to 7 days. The compressive strength values at 28 days of specimens 1-8 were in the range of 0.25-0.32 MPa, and the compressive strength values of specimens 3-8 were > 0.3 MPa. The coefficients of correlation between compressive strength and apparent gravity at 7 days and those between compressive strength and ettringite/Ca(OH)₂ XRD peak intensity at 28 days were above 0.8. That is, the compressive strength exhibited an influence on apparent gravity at 7 days and on hydrate at 28 days. The thermal conductivity of all specimens was 0.041-0.045 W/mK, and the highest value of thermal conductivity was shown by specimen 5. The coefficient of correlation between apparent gravity and thermal conductivity was 0.84. It was concluded that control of raw materials and hydrates must be considered for manufacturing of insulation materials. The cement-based thermal insulation material in this study could be used in construction fields.